The present invention relates to an alumina porcelain composition suitable for use as a dielectric material having stable temperature characteristics, as well as a high dielectric constant and un-loaded Q in the high-frequency range such as the microwave frequency range, particularly at frequencies higher than those in the X-band.
The recent expansion of new media including communications networks such as satellite communications, community antenna television systems, etc., has necessitated the use of broad frequency range including high frequencies approaching the microwave frequencies due to the increased amount of communication information. The X-band has a frequency range of from 8 to 12.4 GHz and is important for satellite communications, radio communications in case of disasters, etc. At the same time, the operating range of dielectric porcelain has expanded to that of the microwave frequencies and it is used in dielectric oscillators and substrates for microwave ICs (integrated circuits), as well as for the purpose of achieving impedance matching in microwave circuits. The demand for dielectric porcelain is increasing because many units there of are necessary for stabilizing the frequency of outputs from filters and the operating frequency of Gunn or FET microwave oscillators.
The minituarization of microwave circuits is another recent trend in the communications field. The size of a microwave circuit is limited by the wavelength of the electromagnetic waves being propagated through a waveguide containing a dielectric material. The wavelength of an electromagnetic wave propagating through a microwave circuit mounted in a waveguide is expressed as .lambda.0/.epsilon., wherein .lambda.0 is the wavelength of the microwave travelling in a vacuum and .epsilon. is the specific inductivity of the waveguide. This expression suggests that a smaller circuit can be realized by using a material with greater .epsilon.. It is therefore desired to produce a dielectric porcelain composition of high dielectric constant, which displays low-loss and stable temperature characteristics.
Conventional dielectric porcelain materials include the ZrO.sub.2 --SnO.sub.2 --TiO.sub.2 and BaO--TiO.sub.2 systems, including systems having some of the foregoing atoms partially replaced by other elements, as well as the combination of a dielectric porcelain or glass having a positive temperature coefficient for specific inductivity and TiO.sub.2 which has a negative temperature coefficient. However, these conventional products have one or more defects, such as low specific inductivity, a small un-loaded Q value, a temperature coefficient outside of the desired range, poor mechanical strength, poor chemical stability, and high material cost.